Barcelona will begin the defence of their Champions League title on Tuesday night against an AC Milan team missing injured forwards Zlatan Ibrahimovic and Robinho.
Barca are aiming to put a domestic slip-up behind them.
On Saturday, Real Sociedad rallied from a two-goal deficit to draw 2-2 with the Spanish champions, handing an early advantage in the Primera Liga title race to Real Madrid, considered to be Barca's only challengers.
While Pep Guardiola's side have started the season by winning the Spanish and European Super Cups, defensive lapses appear to be their foremost problem. However, Milan's normally potent attack is short of forwards with Massimiliano Allegri, the Milan coach, ruling Ibrahimovic - Barcelona's record signing two seasons ago - and Robinho - a former Real player - out.
Ibrahimovic's anticipated return to Camp Nou for the first time since his turbulent exit before last season will have to wait after the Sweden striker, who cost Barca €69 million (Dh346m) from Inter Milan in 2009, injured his hamstring in training. Robinho has yet to recover from a groin injury.
Carles Puyol, the Barcelona defender, should return for the first time since May after recovering from knee surgery, but Gerard Pique is out injured, leaving Eric Abidal to likely fill the other centre-back spot.
"We have to do better and prepare better," Guardiola said after the draw, which began with Lionel Messi, Andres Iniesta and David Villa on the bench.
Barcelona and Milan are favoured to advance out of a group that also includes BATE Borisov of Belarus and the Czech club Viktoria Plzen, who meet tonight in Prague.
Thiago Alcantara, the Barcelona midfielder, said their intensity dropped in the second half of Saturday's draw, showing the team many are comparing with the all-time greats are not invincible.
Milan began their Serie A campaign with a similar slip-up to Barcelona.
However, it was they who came from to clinch a 2-2 draw at home to Lazio on Friday.
"I am calm, it isn't a final, just the first match of the group stages," Allegri said on the club's website yesterday.
"We are playing against a side that has won so much but our aim is to get through the group stages."
Alexandre Pato and Antonio Cassano are Allegri's lone options in attack.
The former Barcelona players Mark van Bommel and Gianluca Zambrotta return to play their former club, with Van Bommel lining up against Xavi and Iniesta for the first time since Spain's 1-0 World Cup final victory over the Netherlands last year.
While that final was remembered for the Dutch team's bruising display, Milan know Barcelona's midfield must be held in check with Cesc Fabregas and Sergio Busquets also to worry about.
"The key players are Xavi and Iniesta - their right brain and their left brain," Kevin-Prince Boateng, the Milan midfielder, said yesterday.
"If you stop them it becomes difficult for their forwards to score.
"Teams can't play without their brains."